The background of the invention relates to a need in the industry for a more or less continuous, and at least a regular, measuring, monitoring and verification of the particle content in an injection water flow in an underwater line. As such, there is a need for a technical solution rendering possible to measure, monitor and verify potential changes in the particle content in the injection water flow over time, but also potential abrupt changes.
In context of water injection into a well, it is common to filter and treat the raw water of the injection water at a shipment site for the injection water before the finally treated injection water is transported onwards to a receiving site for the injection water. The water treatment is carried out in order to obtain a water quality acceptable to the water injection operation of interest. The most elementary water treatment consists in removing inorganic and/or organic solid particles from the raw water through filtering and/or sedimentation (which is more uncommon) of undesirable particles from the raw water. It is also common to treat the raw water chemically at the shipment site. Typically, this shipment site is comprised of a surface installation offshore, for example a bottom-fixed platform or a floating installation, whereas the receiving site is comprised of an injection well and/or a subterranean reservoir, for example an oil reservoir, to which the well is connected in a flow-communicating manner. Such water injection is usually carried out in a subsea well, but it may also be of interest to transport the injection water from the shipment site and further onto a land-based injection well. In both situations, long transport distances may be involved between the shipment site and the receiving site for the injection water.
For such water injection it is customary to take the raw water from a body of water located in vicinity of the shipment site. Thus, the body of water may, for example, be comprised of seawater, or of water from a lake, river, spring or a groundwater occurrence. This raw water may contain inorganic and/or organic particles of different sizes and/or shapes, and of varying amounts and/or distributions. Moreover, the raw water is generally taken from a surface layer of the body of water. However, the water quality in such a surface layer may vary a lot due to weather-dependent and/or seasonal influences. Thus, the particle content in the surface layer may fluctuate due to variations in the temperature, salt content and sediment content of the water, but also due to the current conditions and/or biological activity in the raw water. Typically, such a particle content comprises particles in the form of inorganic weathering products, for example sand-, silt- and/or clay particles, but also organic particles, for example aquatic organisms, including plankton, various bacteria, including anaerobic and sulphate-reducing bacteria capable of generating hydrogen sulphide gas (H2S), and also bacterial film residues and similar.
Besides creating relatively unstable operating conditions and also occasional problematic operating conditions at the shipment site, especially for installations offshore, such fluctuations in the particle content of the raw water may also influence the particle content in, and hence the quality of, the injection water being transported away from the shipment site. This is customary even if the water has been treated, for example filtered, at the shipment site.
If the raw water for the injection water comprises produced water from a separation plant for hydrocarbon fluid, for example crude oil, also the produced water may have a undesirable organic and/or inorganic particle content, including sand-, silt- and/or clay particles, and also various bacteria, bacterial film residues, oil droplets, gas bubbles, etc. Also variations in the particle content of the produced water may influence the quality of the injection water being transported away from the shipment site.
Furthermore, the injection water may contain various corrosion products, for example rust particles, and/or various depositional products, so-called “scale”, from the shipment site and/or the underwater line. Also this may influence the quality of the injection water.
If such undesirable particles are not adequately removed from the injection water, the particles may cause large problems in the underwater line, the injection well and/or in an oil-bearing reservoir to which the well is connected in a flow-communicating manner. Thus, serious corrosion and/or organic fouling may arise in the underwater line and/or in the well. So-called reservoir souring may also arise if the injection water carries along anaerobic bacteria into a subterranean oil reservoir. Moreover, particularly fine-grained solid particles in the injection water may cause reduced permeability in the oil reservoir. This may inhibit the ability of a water-flood front to flow through the reservoir in order to force more crude oil out of the reservoir. By so doing, the efficiency of water injection as a means of achieving increased recovery from the oil reservoir is also restricted.
If possible to carry out online measuring and monitoring of the particle content in the injection water flow in the underwater line, potential changes in the particle content may be detected quickly. Such changes in the particle content may indicate unacceptable conditions at the shipment site and/or may indicate or cause unacceptable conditions in the underwater line and/or at the receiving site. By so doing, it will also be possible, if required or desirable, to measure and monitor the particle content in the injection water flow at several sites along the underwater line. This may be of interest during transport of injection water over large distances, for example from a shipment site offshore and onto a land-based injection well. On the basis of such online measuring and monitoring, it will also be possible to quickly initiate actions that may remedy the negative development at the shipment site, in the underwater line and/or at the receiving site.